Smoking machines are used in connection with the tobacco industry to determine FTC tar and nicotine values of various cigarettes when smoked according to certain standard test conditions. The smoking machine provides for the collection of various substances contained in cigarette smoke. The substances are later fed to an analysis stage.
It is sometimes desirable to determine the performance of various cigarettes when smoked according to non-standard conditions. In this regard, many commercially available smoking machines are meant to measure smoking for specific draw profiles and adjustment is difficult. Moreover, motor-driven multiport machines are often incapable of reproducing some extreme profiles due to the inability of large motors to change speeds rapidly enough. In the extreme case, it is sometimes desirable to replicate accurately the recorded draw profile of a human test subject. Actual human puff profiles represented by a recorded pressure differential as a function of time can be measured as a test subject smokes a cigarette. Essentially, the cigarette is smoked through a tube having a constriction at its intermediate point. The differential between the upstream and downstream pressure can be measured via transducers and this pressure differential recorded digitally as a function of time to provide a puff profile including puff phases wherein the cigarette is being inhaled, and pause or smolder phases wherein the cigarette is not being inhaled.
Equipment for receiving the recorded puff profiles and simulating or mimicking the recorded human smoking behavior on a smoking machine has been described in SMOKING BEHAVIOR by Raymond E. Thornton, Churchill Livington Publishers, 1978, pp. 277-288. The puff profile is converted into an analog signal, which in turn, controls an analog valve between a vacuum chamber and a cigarette, the valves opening or closing more or less depending on the particular values of the recorded draw profile.
U.S. Pat. No. 4,365,640 describes a smoking machine capable of simulating human smoking, based on a recorded draw profile by a different control scheme. A step motor controls the operation of a vacuum cylinder. The stepping motor is controlled by a control circuit which converts an analog signal corresponding to a human draw profile into control signals for the stepping motor. Valves located between the cigarette and vacuum cylinder are also controlled by the control circuit to allow smoke collected in the vacuum cylinder to be exhaled during the smolder phases of the draw profile. A valved bypass is located between the cigarettes and Cambridge filter pads which collect FTC tar and nicotine. During the puffing phase, these valves are closed so that smoke from the cigarettes passes through the filter pads and into the vacuum chamber. During the smolder phase, these valves are opened to communication with the atmosphere to simulate a condition in which the smoker takes the cigarette out of the mouth. The control circuit includes provision for a delay between the inhale cycle and the exhale cycle in order to allow more accurate reproduction of "double draw" puffs. D.E. No. 3236593 discloses a smoking machine having a movable element between the smoking article and the vacuum source. The magnitude of inhalation cycle can be controlled by positioning of the movable element or valve.
The known programmable smoking machines such as those described above are dependent on motor speed changes for reproduction of a puff profile. Inertial, mechanical, electrical and magnetic resistance to speed changes result in inherent difficulties in accurately duplicating puff profiles, particularly with respect to rapidly changing portions thereof. In addition, known control systems for such smoking machines suffer various drawbacks, including ease of modification, accuracy of control and the like. Further, methods used by such machines to duplicate recorded draw profiles do not always accurately reproduce the physical smoking conditions of the recorded draw profile. In addition, use of some motor-driven systems involves inherent capacity or accuracy limitations in that the number of ports, i.e., the number of cigarettes which can be smoked simultaneously, must be limited or accuracy must be sacrificed.